Macrocyclic Donor–Acceptor Dyads Composed of a Perylene Bisimide Dye Surrounded by Oligothiophene Bridges

Abstract Two macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide (PBI) dye have been synthesized via a platinum‐mediated cross‐coupling strategy. The crystal structure of the double bridged PBI reveals all syn‐arranged thiophene units that completely enclose the planar PBI chromophore via a 12‐membered macrocycle. The target structures were characterized by steady‐state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Both donor–acceptor dyads show ultrafast Förster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent.

S3 solvent resonances or natural abundance carbon resonances. Multiplicities are reported as s = singlet, brs = broad singlet, d = doublet, dd = doublet of doublets, t = triplet, dt = doublet of triplets, q = quartet, quin = quintet, sex = sextet, m = multiplet with the chemical shift in the center of the signal.
UV/Vis absorption spectra were recorded for solutions in cuvettes (SUPRASIL®, Hellma® Analytics) on a Jasco V-670 or V-770 spectrometer and fluorescence spectra on a FLS980-D2D2-ST fluorescence spectrometer (Edinburgh Instruments) and were corrected against the photomultiplier sensitivity and the lamp intensity.
CV and DPV experiments were carried out with a BASi Epsilon potentiostat connected to a microcell apparatus from rhd instruments involving a 1.6 mL sample container, a platinum counter-and pseudo-reference electrode as well as a glassy carbon working electrode.
Single crystal X-ray diffraction data were collected at the P11 beamline at DESY. The diffraction data were collected by a single 360° scan ϕ sweep at 100 K. The diffraction data were indexed, integrated, and scaled using the XDS program package. [S1] In order to compensate low completeness due to single-axis measurement, two data sets were merged using the XPREP program from Bruker. [S2] The structures were solved using SHELXT, expanded with Fourier techniques and refined using the SHELX software package. [S3] Hydrogen atoms were assigned at idealized positions and were included in the calculation of structure factors. All non-hydrogen atoms in the major disorder part of main residues were refined anisotropically. In the crystal structures some of the side chains were disordered and modelled with restraints and constraints using standard SHELX commands RIGU, DELU, ISOR, SADI, SAME, DFIX, DANG, FLAT, SIMU, CHIV and EADP. The solvent molecules in the solvent accessible voids also had disorder and were restrained and/or constrained by a similar set of instructions.
The transient absorption spectrometer setup is based on a femtosecond laser "Solstice" from Newport-Spectra Physics with a fundamental wavelength of 800 nm which provides 100 fs long pulses with a repetition rate of 1 kHz. This laser source was used to pump a NOPA to generate the excitation pulses at 530 nm with a pulse length of around 50 fs. The FWHM-bandwidth of the excitation pulse was 8.5 nm and the pulse energy was set to 20 nJ ((5T)2-PBI) and 15 nJ (5T-PBI). Wire grid polarizers S4 were used to set the pump pulse polarization to 54.7° in relation to the horizontal polarized white light continuum to achieve magic angle conditions. Another part of the laser beam was guided to a TOPAS-C from Light-Conversion to obtain a wavelength from 1260 nm ((5T)2-PBI) and 1000 nm (5T-PBI) which was used to generate the probing white light continuum within a moving CaF2 ((5T)2-PBI) or sapphire crystal (5T-PBI). To achieve the probe range from 450 nm to 915 nm a dielectrically coated quartz glass short pass filter with 950 nm, thickness 3 mm, from Edmund-Optics were used. The sample was dissolved in spectroscopic grade dichloromethane from ACROS organics and the solution was filled in a quartz glass cuvette with an optical path length of 0.2 mm ((5T)2-PBI) and 2 mm (5T-PBI). The optical density at the excitation wavelength was set to 0.055 for (5T)2-PBI and 0.50 for 5T-PBI. The IRF was ca. 80 fs as measured for stimulated Raman signals of the solvent. Further details on this spectrometer setup are provided in ref [S4] .
Spectroelectrochemical experiments were performed on a Cary 5000 UV/Vis/NIR Spectrometer from Agilent in combination with a sample compartment consisting of a custom-made cylindrical PTFE cell with a sapphire window and an adjustable three in one electrode (6 mm platinum disc working electrode, 1 mm platinum counter and Ag/AgCl leak free reference electrode) in reflection mode. The optical path was adjusted to 100 μm with a micrometer screw. Potentials were applied with a reference potentiostat PAR 283 from Princeton Applied Research. Upon applying a new potential to the solution an equilibration time of 20 seconds between each measurement was employed.

S16
Single Crystal X-ray Analysis  Figure S2. a) Front view of a single (5T)2-PBI centrosymmetric molecule A (ORTEP drawing in 50% probability for thermal ellipsoids). PBI chromophore is coloured in red, macrocycle in blue and solubilizing alkyl chains in grey. Crystal packing seen approximately along the a-, c-, and b-axes for b), c) and d), respectively. Heavily disordered aliphatic chains as well as solvent molecules were omitted for clarity. Figure S3. a) Front, b) side and c) top view onto the unsymmetric molecule B of (5T)2-PBI. Heavily disordered aliphatic chains as well as solvent molecules were omitted for clarity. d) Unit cell including all structural disorder (violet) and aliphatic chains (grey). The ellipsoids are set to 50% probability.

DFT Calculations
Rotational Barrier: To estimate the rotational barrier ( Figure S4) of the imide substituent of 8, calculations were conducted only on one half-segment, namely the naphthalene imide part ( Figure   S4b). In order to estimate the energy cost of this rotation a dihedral angle scan of α in 0.5° intervals was performed ( Figure S4a). Here, the change of the total energies ∆E depending on the torsion angle α is plotted. This angle α, which was modified during the scan, is highlighted in Figure S4c. The initial α of 90° between the phenyl substituent and the naphthalene monoimide core was readily reduced until complete rotation of the substituent. In the starting geometry ( Figure S4c) the sulphur atom points away from the naphthalene imide core, whereas during the rotation this subunit undergoes a conformational change at α = 59° ( Figure S4d) towards the core due to the repulsive hydrogen-core interaction. Further rotation up to -26° leads to an outer plane uplifting of the nitrogen atom ( Figure S4e) and an almost perpendicular angle between the thiophene and the phenyl group. This geometry also resembles the structure with the highest total energy level during the entire rotation process and therefore the closest structure to the "real" transition state (TS). This geometry was the basis for the TS calculation of which the result is shown in Figure S4f. The energy difference between this TS geometry and the fully relaxed monoimide is 114 kJ mol −1 and can therefore be considered as the rotational barrier or the Gibbs free energy of activation Δ ‡ . To determine the half life time of the rotation event the reaction rate krot according to Eyring has to be determined first (Eq. 1) Here kB is the Boltzmann constant, T the temperature R and h the Planck constant.
The half life time t1/2 (Eq. 2) can be calculated by the following equation: / . ( The results of t1/2 = 30 days at room temperature (25 °C) and around 51 min at 75 °C show the importance of elevated temperatures during the final macrocyclization reaction towards 5T-PBI. [S9] Figure S4. a) Plot of the change in total energy ∆E against the dihedral angle α. b) Chemical structure of the molecular fragment used for the calculations. c) Geometry optimized structure of the starting geometry for the rotational scan and the starting angle α incorporated by the planes of the naphthalene (red) and phenylene (blue) subunit. d) Geometry with α = 59 °e) Highest energy geometry with α = 26 °. f) Geometry of the TS. All calculations were conducted with DFT at the B3LYP/6-31G(d) level of theory. Strain energies: The strain energies of the macrocycles (5T)2-PBI and 5T-PBI were calculated as follows: The connecting C-C bonds between two thiophene units of the bridges were removed virtually from the optimized geometries of (5T)2-PBI and 5T-PBI and the obtained radicals were saturated by thiophene capping molecules to retain the local S20 environment of the two ends. Geometry optimization leads to the lowest energy conformation of the resulting structures and complete macrocyclic induced strain release of both subunits. Figure S6 shows the optimized geometries of these open macrocycles 11 and 12 as well as capping bithiophene 13. Figure S6. Front view of the optimized geometries of the non-cyclic structures 11 and 12 as well as bithiophene 13. The quantum mechanics calculations were carried out on the level of B3LYP density functional with the 6-31G(d) basis set as implemented in with Gaussian 16. Aliphatic chains were replaced by methyl groups. Color code: carbon = light grey, hydrogen = white, nitrogen = blue, oxygen = red, sulfur = yellow.